Identification of Immunoreactive Epitopes of HTLV I and Their Potential Applications to a Subunit Vaccine Human T-cell lymphotrophic virus type I (HTLV-I) is the causative agent of an aggressive form of T-cell leukemia endemic to certain geographic areas but also currently increasing in frequency in the same population at risk for developing AIDS. Sero-epidemiologic data suggest the presence of a type-common neutralization determinant. This proposal seeks to identify and produce, by use of a recombinant DNA expression system, HTLV-I encoded epitopes to assess their effect on in vitro measures of infectivity and virus neutralization. Immuno-reactive epitopes characterized in this manner have potential application to eventual production of an HTLV-I subunit vaccine.